The value of a jewel or ornament made of precious metal depends at least partly on its material composition. It is not unusual to alloy cheaper materials with e.g. gold, and still sell the final product at a price that would only be justified if the material was solid gold. Another commonly used trick is plating an object made of cheaper materials with a thin layer of gold or other precious metal. Pricing might be more transparent if a cheap, simple and reliable way was available for determining the material composition of such a sample. Non-destructiveness is a strict prerequisite in such applications, because not only the material composition but also the visual appearance and integrity of the sample typically plays a major role in determining its value.
Non-destructive composition analysis of jewels and other corresponding delicate samples has also other applications than preventing cheating. Gemstones having a common geological origin carry a “fingerprint” of their origin in their composition. Minor traces of impurities tend to appear in similar mutual relations in gemstones coming from the same mine. By analyzing the material composition it is possible to deduce, from which source does a sample come from, which has important applications in e.g. tracking stolen or other illegally transported jewellery.
Microanalysis is closely related to non-destructive analysis of delicate samples, because microanalysis means analyzing the material composition of sample objects that are so small and/or so few that they must be treated very carefully. Microanalysis is needed for example in crime scene investigation to trace the origin of fibers, paint flakes or other small pieces of evidence. Other applications of microanalysis include, without being limited to, quality control of industrial processes, determining the contents of inclusions in geology, and tracking the origins of impurities in semiconductors.
Traditional methods of composition analysis have been chemical. A small chip of a metal jewel has been cut off and subjected to interaction with various chemical compounds under microscope. A drawback of such methods is that they are not completely non-destructive: the chip has to be taken from a place where the cutting trace will be least visible. Additionally chemical analysis is relatively slow and may require the use of strong acids and other hazardous substances.
Microanalysis has traditionally required the use of vacuum chambers, electron beams and other kinds of complicated technical equipment, which dictates that it has only been feasible for use in a sophisticated laboratory environment.
Other known composition analysis methods are X-ray fluorescence analysis and optical emission spectroscopy. Of these, in the former it is difficult to achieve the required energy resolution; for example the K-alpha line of copper and the K-beta line of zinc are so close to each other that these two important alloying metals are difficult to separate from each other. Optical emission spectroscopy requires a part of the sample substance to be heated to a state of plasma, which has traditionally been achieved by igniting an electric spark between the sample surface and an electrode in the measurement apparatus. The electric discharge and local heating eat into the material surface so badly that a very clearly visible crater is produced, which means that the method is far from non-destructive.